Stabilized polyolefins



United States Patent 3,337,495 STABILIZED POLYOLEFIN S John M. Corbett, Midland, Mich., and David A. Gordon,

Scarsdale, N.Y., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Nov. 18, 1963, Ser. No. 324,179 Claims. (Cl. 260-4535) This invention relates to new and improved polyolefin compositions which are stabilized against oxidation and color changes.

Polyolefins, such .as polyethylene, polypropylene and .the like, are commonly subjected to elevated temperatures in the course of their handling and processing into useful items of commerce. Such processing methods as rolling,

where color is often a critical factor.

It is known to the art for example, that phenolic compounds, particularly those having a substituted bisphenol structure, such as alkylidene-bis(alkyl phenol)s,

are extremely effective antioxidants when incorporated into polyolefins such as polyethylene and polypropylene. The stabilizing efiiciency of these compounds is synergistically increased when they are used in combination With auxiliary antioxidants such as a dialkyl ester of thiodipropionic acid. However, such phenolic stabilizing compositions when used singly or in combination with auxiliary antioxidants have the disadvantage of discoloring the .olefin polymer upon incorporation, and the discoloration is rapidly intensified upon exposure to oxidative conditions.

In accordance with the present invention, both the oxidation and color stability of phenolic stabilized polyolefins are improved by the addition of a minor proportion of a polypentaerythritol to the stabilized polyolefin composition.

a It is an object of this invention to provide polyolefin materials having improved oxidative stability.

Another object of this invention is to provide stabilized olefin polymers, particularly polyethylene and polypropylene, which are resistant to color deterioration and are stable against oxidation.

A further object is to provide such stabilized compositions which comprise phenolic stabilizers and which are resistant to color deterioration.

These and other objects are accomplished by incorporating into a polyolefin composition a small but efiective amount, usually between about 0.01% and about 1.0% by weight, of 'a polypentaerythritol having the formula CHzOH L HrOH in wherein n is an integer from 1 to 13.

Polypentaerythritols, as is known to those skilled in the art, are those alcohols which are higher derivatives of pentaerythritol and which are joined by etherification of one or morehydroxyl groups of pentaerythritol with other pentaerythritol residues. Polypentaerythritols include dipentaerythritol, tripentaerythritol, tetrapentaerythritol, pentapentaerythritol, heptapentaerythritol, octapentaerythritol, nonapentaerythritol, decapentaerythritol, similar polypentaerythritols and mixtures thereof.

The polypentaerythritols are prepared by any of the well-known procedures of the prior art. Such illustrative procedures are found in US. Patent Nos. 2,462,049 and 2,552,532.

In accordance with this invention, these polyols may be used singly or, often because of their commercial availability, in mixtures containing various amounts of at least two such polyols such as dipentaerythritol and tripentaerythritol.

The polypentaerythritolsof the present invention are generally used in an amount between about 0.01% and about 1% by weight, based on the weight of the whole polyolefin composition. Preferably, the amount employed is between about 0.03% and about 0.2% by weight, especially in polyolefin compositions such as polyethylene and polypropylene.

The polypentaerythritols used in the practice of this invention are generally employed in conjunction with other known additives, such as phenolic antioxidants and heat stabilizers, and other known additaments generally used for polyolefin compositions.

The polypentaerythritol stabilizers can be incorporated or blended, along with other stabilizers, into polyolefin compositions by any of the conventional methods used for blending such materials into resins or plastics. Typical of such methods that can be suitably employed include milling on heated rolls, deposition from solvents, and dry blending. The polypentaerythritol can be incorporated separately or together with the other stabilizers into the polyolefin composition. 7

The phenolic compounds employed in the practice of the present invention are organic compounds which contain an aromatic radical and at least one hydroxy group linked to a carbon atom embraced in the nucleus of the aromatic radical. The phenolic compound may be monohydric or polyhydric, and one or more hydrogen atoms of the aromatic nucleus may be substituted by organic radicals. Representative phenolic stabilizers include butyl phenol, secondary butyl phenol, tertiary butyl phenol, amyl phenol, octyl phenol, nonyl phenol, decyl phenol, dodecyl phenol, octadecyl phenol, oleyl phenol, cardanol, 2,4-didodecyl phenol, 2,4-dibutyl phenol, 3,5-diamyl phenol, dinonyl phenol, didodecyl phenol, di-t-butyl-omethyl phenol, di-t-butyl-p-methyl phenol, o-phenyl phenol, p-phenyl phenol, 2-methyl-4-tollyl phenol, 2,4-dimethyl-S-phenyl phenol, p-benzyl phenol, 2-t-butylm-cresol, o-t-butyl phenol, 2,6-di-t-butyl phenol, 2,6-diethyl phenol, 2,4,6-tri-t-butyl phenol, t-butyl-hydroquinone, 2,5-di-t-butylhydroquinone, o-octyl phenol, and tert-butylcatechol.

Preferred phenolic stabilizers are compounds having a substituted bisphenol structure such as the alkylidene-bis- (dialkylphenols) of which representative examples are 4,4-cyclohexylidene-bis-(Z-tert-bntylphenol), 4,4-isopropylidene-bis-(Z-tert-butylphenol, and 4,4-butylidene-bis- (6-tert-butyl-m-cresol); and the alkylidene-bis-(cycloalkylphenols) such as 4,4'-cyc1ohexylidene-bis-(Z-cyclohexylphenol), 4,4'-sec-butylidene-bis (2 cyclohexylphenol), 4,4-(l-methylhexylidene) bis (2 cyclohexylphenol, 4,4-cyclopentylidene-bis-(Z-cyclohexylphenol), 4,4- methylene-bis- 2-cyclohexylphenol) 4,4-isopropylidenebis- (Z-cyclohexylphenol) Auxiliary antioxidants which may be synergistic in function with the phenolic stabilizers such as the dialkyl esters of thiodipropionic acids may also be employed. Exemplary of these esters are the dimethyl, diethyl, dilauryl, etc., esters of thiodipropionic acid.

The olefin polymers employed in the practice of the present invention are any solid, high molecular weight Table I. The concentrations of additives is based on the weight of the polypropylene.

The procedure described above was repeated. This polymers of olefins containing two or more carbon atoms. 15 m Samples Yf stbflizer combinations with and Exemplary of these polymers are polyethylene, polyprowithout the addition of dipentaerythritol were used for pylene pOh/(Lbutene), poly(l pentcne) poly(3 methyl comparative purposes. The color of the samples was ob- LbuteneL p01y( 4 methyl l pentene), polystyrene em served periodically and rated according to a numer cal copolymers of Such olefins as, for example, ethy1ene scale. On this scale the higher the numerical color rating, propyleng, ethylenebutene, etc. may likewise be 20 the darker or more discolored the sample. For example, ployed 1 1s colorless, 7 is light tan, 12 is dark yellow tan. The In order to more fully illustrate the invention, the folresults of color evaluatlons are summaflzed by the lowing experimental data are given data set out in Table II. In Table II CBCP 1s 4,4'-cyclohexylidene-bis-(2-cyclohexylphenol); DLTDP is dilauryl Example I 25 3,3'-thiodipropionate; TLP is trilauryl phosphite; ZnSt is A quantity of about 500 grams of granular, essentially Zinc stearate; MgSt is magnesium stearate; and dipenta is linear, polypropylene having a melt index of about 3 was dipentaerythritol.

TABLE II Additives in Polypropylene (percent) Color Rating at 150 C. Test No. Oven Exposure (hours) Oven-Lite (hours) CBCP DLTDP TLP ZnSt MgSt Dipenta 20 100 200 300 0. 0. 25 0 5 9 9 1,6101,870 0. 05 0. 1 1 2 a 3 1,6101,870 0. 05 0. 25 1 1 2 2 3 1,6101,870 0. 05 0. 25 1 1 2 3 3 moo-1,320 0. 05 025 1 1 2 3 3 1,450-1,470 0.01 3 ND ND ND ND 0-20 1 0. 25 2 5 s 8 ND 280-300 0. 01 0. 25 3 5 7 s 9 1,300-1,420 0. 01 0.25 1 1 1 3 4 1,500-1,5s0 0. 01 0. 25 0.10 a 6 8 9 10 1,550-1, 580 0. 01 0. 25 0.10 1 1 2 a 4 1,6001,660 0. 01 0. 25 0.05 1 1 1 3 4 1,520-1,540 0. 01 0. 25 0.10 1 2 5 6 s 1,100-1, 120 0. 01 0. 25 0.10 1 1 2 5 0 1,840-1,860 0. 01 0. 25 0.10 2 2 7 7 s 1,820-1,840 0. 01 0. 25 0.10 1 1 1 2 2 1, 5601,580

ND =Not determined.

stirred in an open container with about 200 ml. of a methylene chloride solution of the additive or additives to be tested. Stirring was continued until nearly all the methylene chloride was evaporated and the additive had been thoroughly dispersed through the polymer. The treated polypropylene was dried at C. under nitrogen in a vacuum oven for about 4 hours. The additive (or mixture of additives) was then further mixed with the polymer by extrusion at about 250 C. The extruded plastic, after being converted into pellet form for handling, was then compression-molded at about 230 C. into 100 ml. thick samples. These test pieces were exposed in a circulating air oven at 150 C. and were examined periodically until the first signs of degradation were noted. This oxidative degradation appeared in the formation of spots of powdery disintegration of the solid structure and was associated with a slight darkening of the polymer. The time in hours to reach this point is referred to as the oven-life and where two figures are given in the following table for a particular composition, these are respectively the time of the last observation when the sample appeared unchanged and the time of the next observation when signs of degradation were first seen.

Some representative test results employing a phenolic compound exhibiting antioxidant activity are tabulated in Example I] Stabilized test samples were prepared using the procedure of Example I wherein the base polymer was high density polyethylene. Color evaluation tests were conducted following the procedure of Example I, with the exception that the temperature of the circulating air oven was lowered to C. The results of these tests are summarized in Table III below. In Table III CBCP is 4,4- cyclohexylidene-bis(Z-cyclohexylphenol); DLTDP is dilauryl 3,3'-thiodipropionate; dipenta is dipentaerythritol; and tripenta is tripentaerythritol.

TABLE III Additives inPolyethylene (percent) Color Rating at 100 0. Test No. Oven Exposure (hours) CBCP DLTDP Dipenta 'lripenta 20 125 250 500 N OTE.1 is less than 1; 1= is much less than 1.

Example III 5 The data recorded in Table IV show that incorporation Stability and color deterioration evaluationswere conof dlpentaerythntol m phenolic Stablhzed polypiopylene ducted with stabilizer modified polypropylene to which test numbers 2, 13) substantially retards the discoloravarious polyhydric compounds were incorporated to dem- :g :i f gig l g ggi i giq z i figi i onstrate the unexpected eflicacy of the polypentaerythria i 0 r a i t S f tols. The procedure of Example I was repeated in the 33 0 er Po y y m compoun S es ers preparation of the test samples. Two stabilizer systems E I IV were evaluated. The first, designated as stabilizer Sysxamp e tern A, was comprised of 0.05% CBCP, 0.50% Comparative evaluation tests were made with stabilizer DLTDP, 0.10% TLP, and 0.05% zinc stearate. The poly- System B of Example III, following similar procedures, hydric compound was included in the polypropylene at a with the exception that the polyhydric additives were inconcentration of 0.05% based on the weight of the polycorporated in the polypropylene at a concentration of mer. The second designated stabilizer System B, was 0.10% based on the weight of polymer. The temperature comprised of 0.05 CBCP and 0.25% DLTDP. The of the circulating air oven was lowered to 100 C. The repolyhydric compound was included in the-polypropylene sults of the evaluation tests are summarized bythe data at a concentration of 0.10% based on the weight of the set out in Table V following.

TABLE V v Color Rating at C. Oven Stabilizer Exposure (hours) Test N0. System Polyhydric Additive B None (Control 4 7 9 10 B Dipentaerythritol 1 1 3 3 B Sor itol l -r 2 5 6 5 B Diethylene glyc 4 5 6 9 B Pentaerythritol 1 4 5 5 B Polyethylene glycol [HO (OZH4O)11O2H4OH] average molecu- 1 5 6 10 lar weight 400. ,p B Polypropylene glycol [HO(C3H80)|1C2H6OH1 average molecl 7 9 1O ular weight 400. r B Polypropylene glycol, average molecular weight 1200 B Polybutylene glycol [HOC4H5O) amnion average molecu- 3 5 7 8 lar weight 500. B N eopentyl glycol 4 5 6 8 B Pentaerythritol rerraar-Pmm 4 7 8 9 B Citric Acid 6 a s 9 polymer. The results of the evaluation tests are summarized by the data set out in Table IV below.

TABLE IV The data recorded in Table V show that incorporation of dipentaerythritol in phenolic stabilized polypropylene Stabilizer Polyhydric Additive System Color Rating at C. Oven Exposure (hours) None (Control)- Dipentaerythntol.

Pentaerythritol- Sorbrtol Tartaric Acid. Citric Acid Mandelic Acid.

None (Control) Dipentaeryrhrirnl Citric Acid wwewwe ular werg t Neopentyl glycol Diethylene glycol: Polybutylelrlre 'figgcol [HO (CJIaO) nCtHiOH] average molec- Pentaerythritol tetraacetate 7 (test number 2) substantially retards the discoloration of the polymer when contrasted with polypropylene containing no color retardant additive (test number 1) or other polyhydric compounds (test numbers 3-12).

Example V Comparative coloration and oxidative stability evaluation tests were made using some bisphenol stabilizer systerns. Polypropylene was employed as the base polymer and sample preparation and testing procedures were identical with Example I. The results of the evaluation tests are tabulated in Table VI following. DLTDP is dilaury-l 3,3'-thiodipropionate.

TAB LE VI Color Rating at 150 C. Oven Exposure (hours) Test No. Stabilizer System (A) 0.05% 4,4-isopropyl' ene-bis-(Z-tert-butyl- 4 4 4 4 6 phenol) +0.25% DLTDP. (B) A-l-0.10% dipentaerythritol 2 3 3 3 3 r (C) A+0.10% tripentaerythritol 2 2 2 3 4 (D) 0.05% 4,4-butylidene-bis-(ti-tert-butyl-m- 2 3 4 5 7 cresol) +0.25% DL'I'DP. (E) D+0.10% dipentaerythritol 1 1 1 3 4 (F) D+0.10% tripentaerythrito 1 1 1 3 6 (G) 0.05% proprietary phenolic co ation product 3 5 9 10 10 (Topanol CA-Arnold Hofiman Co.) +0.25% DLTDP. 8...., (H) G+0.10% dipentaerythritol 1 1 2 3 4 Nora-Tests 1, 4, and 7 are not examples of the invention.

Example VI Comparative coloration evaluation tests were made as in Example V, with the exception that the oven temperature was lowered to 100 C. The results of the evaluation tests are summarized in Table VII which follows. DLTD'P is dilauryl 3,3-thiodipropionate.

TABLE VII directly to the aromatic nucleus of an aromatic hydrocarbon as the only substituent of such hydrocarbon, which composition is predisposed to discolor upon exposure to oxidative conditions, and, as an agent improving the resistance of the phenolic-stabilized composition to color deterioration, from about 0.01% to about 1% by weight Test No. Stabilizer System Color Rating at 100 C. Oven Exposure 0.05% 4,4-butylidene-bis-(6-tert-butyl-m-eresol) 0.25% DLTDP.

A+O.10% dipentaerythritoL. A+0.10% tripentaerythritol 0.05% proprietary phenolic condensation product D (E) D+0.10% dipentaerythritol (hours) N0'rE.Tests A and D are not examples of the invention.

Example VII Stabilized test samples of polyethylene were prepared using the procedure of Example 1. Color evaluation tests were conducted with 2,6-di-tert-butyl-p-cresol (DtBpC). The results of the evaluation tests are summarized in Table VIII.

based on the composition of a polypentaerythritol having the formula:

where n is an integer from 1 to 13.

TABLE VIII Color Rating at C. Oven Exposure (hours) Test No. Stabilizer System Y 0.05% DtBpC 6 7 7 7 7 0.05% DtBpC, 0.05% dipentaerythritol 1= 1- 1- 1- 1 0.05% DtBpC, 0.05% tripentaerythritol 1- 1- 1- 1- 1 N OTE.-l is less than 1; 1= is much less than 1;

2. The composition of claim 1 in which the polymer is selected from the group consisting of polypropylene and polyethylene, the phenolic antioxidant is selected from the group consisting of 4,4-cyclohexylidenebis (2- cyclohexylphenol), 4,4'-isopropylidenebis (2-tert.-butylphenol), 4,4'-butylidenebis (6-tert.-butyl-m-cresol), and 2,6-di-tert.-butyl-p-cresol, and the polypentaerythritol is selected from the group consisting of dipent aerythritol and tripentaerythr-itol.

3. The composition of claim 1 in which the polymer is polypropylene.

4. The composition of claim 1 in which the polymer is polyethylene.

5. The composition of claim 1 in which the polypentaerythritol is dipentaerythritol.

6. The composition of claim 1 in which the polypentaerythritol is tripentaerythritol.

7. The composition of claim 1 in which the polypentaerythritol is tetr-apent-aerythritol.

8. The composition of claim 1 wherein the phenolic antioxidant is 4,4-cyclohexylidenebis (2-cyclohexylphe- 1101).

9. The composition of claim 1 wherein the phenolic antioxidant is 4,4'-butylidenebis (6-tert-butyl-m-cresol).

10. The composition of claim 1 wherein the phenolic antioxidant is 2,6-di-tert.-butyl-p-cresol.

References Cited UNITED STATES PATENTS 2,943,070 6/1960 Hecker et a1. 260-4595 2,985,617 5/ l961 Salyer et 'al. 260-4595 3,124,555 5/1964 Brown et a1. 26045.95 3,142,659 7/1964 Buckley 260-4595 DONALD E. CZAI A, Primary Examiner. LEON J. BERCOVITZ, Examiner.

H. E. TAYLOR, Assistant Examiner. 

1. A PHENOLIC STABILIZED COMPOSITION OF A SOLID POLYMER OF A MONO-1-OLEFIN HAVING NOT MORE THAN EIGHT CARBON ATOMS CONTAINING A STABLIZING AMOUNT OF A PHENOLIC ANTIOXIDANT HAVING AT LEAST ONE HYDROXY GROUP LINKED DIRECTLY TO THE AROMATIC NUCLEUS OF AN AROMATIC HYDROCARBON AS THE ONLY SUBSTITUENT OF SUCH HYDROCARBON, WHICH COMPOSTION IS PREDISPOSED TO DISCOLOR UPON EXPOSURE TO OXIDATIVE CONDITIONS, AND, AS AN AGENT IMPROVING THE RESISTANCE OF THE PHENOLIC-STABILIZED COMPOSITION TO COLOR DETERIORATION, FROM ABOUT 0.01% TO ABOUT 1% BY WEIGHT BASED ON THE COMPOSITION OF A POLYPENTAERYTHRITOL HAVING THE FORMULA: 